How do you transferr square feet into linear feet?

Question

I needed 14- 7"x3' stair risers. I pondered 1x8x8 ft pine boards, but this multiple density fiber board was boasted cheaper at 1.10 a linear ft. I got a 1x12"x16 ft mdf board that cost $50 and I got four rises.

Answer 1

You don't, you need to find out what the width of the fiber board they're selling is, then divide the total area you need by that number in order to figure out how many "linear feet" to buy.

it's like buying "yards" of fabric, you get the total area by knowing how wide the roll of fabric is.

Answer 2

I don't really understand the dimensions here.

If you needed 14 pieces each 3 foot long, then you need 42 linear feet (7" wide).

If the mdf board was really $1.10 per linear foot, then a 16 foot long piece would cost $17.60. Your 16 foot long board cost $50, or $3.125 per linear foot.

You cannot convert linear feet into square feet or vice-a-versa unless you choose a width for the linear foot piece.

In this case, the width you needed was 7". The area you needed was 14*7"*36" = 3528 sq inches (or 24.5 sq ft).